Marine soundscape as an additional biodiversity monitoring tool: A case study from the Adriatic Sea (Mediterranean Sea)

Abstract

Acoustic monitoring can provide essential information on marine environments, including insights into ecosystem functioning and marine biodiversity monitoring. However, data on species acoustic behavior and ecoacoustics studies in the Mediterranean Sea are still extremely scarce and this limits our ability to use soundscape features in monitoring studies. Here we present the results of a soundscape investigation conducted on shallow hard bottoms of the Adriatic Sea (Central Mediterranean basin). We report the presence of diverse circadian rhythms recorded in two different months, July and September. A power spectral density (PSD) was used to assess the overall spectral composition over time, and the Acoustic Complexity Index (ACI), was identified as a proxy for marine sounds of biological origin. The dominant component of the biological soundscape was composed of snapping shrimps and fishes. Spectral characteristics varied significantly both daily and between the two months. For frequencies >620 Hz (i.e., associated to snapping shrimp activity), both PSD and ACI were higher in July than in September. The same circadian rhythm was reported in both sampling periods, with the presence of snaps for 24h a day, but with significantly lower intensity during daylight hours and pitches at the beginning and ending of the night. At lower frequencies (i.e., <620 Hz), fish vocalizations mostly occurred during the night. Higher values of ACI were recorded during the night in both months, whereas the presence of anthropogenic noise caused opposite results in PSD levels. Noise was associated with higher PSD and ACI at the peak frequency of the snaps, suggesting a stimulation in snapping activity. Our findings provide new insights on the marine biological soundscape and on the potential use of ecoacoustics in future monitoring programs.

Underwater Soundscape Monitoring and Fish Bioacoustics: A Review

“…A few studies have applied soundscape measurements to estimates of biodiversity in terrestrial ecosystems [23,42]. Recently, this approach has also been extended to underwater habitats [21,43]. Based on preliminary studies suggesting that sound intensity is higher on healthy reefs than degraded ones [44], soundscapes have the potential to serve as a monitoring tool for ecosystem health.…”

“…Across a total of 60 studies examined in this review, 34 different metrics and/or indices were selected and analyzed. Power spectral density (PSD) was the most commonly used [3,7,[17][18][19]21,22,38,43,46,59,61,63,64,[66][67][68]. Sound pressure level (SPL), or root mean square (RMS)-SPL, were the next most frequently used parameters [6,8,11,17,20,21,38,53,54,59,61,63,64,68,69].…”

“…Most of the studies testing the robustness of these indices were performed in terrestrial ecosystems, the data of which are not directly comparable to data from underwater acoustics. Similar studies need to be conducted in marine ecosystems [19,22,43,61,76,77]. Each of these indices has different advantages and limitations.…”

“…The most widely used of these newer indices is the acoustic complexity index (ACI) [1,19,22,38,42,43,61,71,75,78,79]. The ACI was developed with the goal of producing a fast and direct quantification of acoustic sounds by focusing on intensity [42].…”

Ecoacoustics: A Quantitative Approach to Investigate the Ecological Role of Environmental Sounds

“…Moreover, ACIt f has been used to investigate animal phenology [89,90] and to estimate the effect of anthropogenic noise [91]. This index has also been demonstrated to be a good proxy of richness and diversity of the communities in forest areas [74,92] and marine and freshwater systems [93][94][95]. The graphic representation of ACIt f depicts the acoustic signature.…”